Brake System Vacuum Source Test
Special Tools
CH-558-A Pressure Gauge
For equivalent regional tools, refer to
Special Tools .
Note:
| • |
Engine
temperature, accessory load, and elevation level will affect engine
vacuum. |
| • |
Vacuum readings
will decrease by approximately 2.7 kPA (0.8 in Hg)
for every 305 m (1000 ft) of elevation above sea
level. |
| Definition: If the brakes on diesel engine
vehicles are operated for a long period of time, e.g. when
approaching traffic lights or a traffic jam, the vacuum may be used
up. The pedal travel is shortened, but will quickly return to the
original pedal travel once the vacuum has been built up. Drivers
often describe this phenomenon as follows: "When the brakes are
operated for a long time, the brake pedal goes right to the floor"
and/or as "Spongy brake pedal". On diesel vehicles, this is no
cause for concern, as the pressure in the brake system is rising at
this point. This can be demonstrated by connecting
CH-558-A gauge (1) to the brake calliper |
| 1. |
Reduce negative air pressure
in brake booster |
| |
Press brake pedal repeatedly |
| |
• |
Press down brake pedal and
maintain pressure |
| Definition: The brake system is operating
correctly if the brake pedal drops further. If the brake pedal does
not drop further, the vacuum system (vacuum line, non-return valve)
must be checked. If no fault can be found there, replace the power
brake booster. Refer to
Power Brake Booster Replacement . |
|
